DENGUE AND DENGUE HAEMORRHAGIC FEVER (DF/DHF)
16 Feb 2007

Dengue fever is a mosquito-borne infection which in recent years has become a major international public health concern. Dengue is found in tropical and sub-tropical regions around the world, predominantly in urban and semi-urban areas.

Dengue is a disease caused by any one of four closely related viruses (DEN-1, DEN-2, DEN-3, or DEN-4).

Both Aedes aegypti and Aedes albopictus have been identified from almost all the islands of Maldives. However, aegypti has been considered as the main vector for the transmission of dengue in Maldives which is confined to the domestic environment while albopictus mostly breeds in peripheral areas.

Infectious agent

The viruses of dengue fever are flaviviruses and include serotypes 1, 2, 3 and 4 (deng 1, 2, 3 and 4). The same viruses are responsible for dengue hemorrhagic fever.

Reservoir

Humans are the main amplifying host of the virus, although studies have shown that in some parts of the world monkeys may become infected and perhaps serve as a source of virus for uninfected mosquitoes.

Mode of transmission

Dengue viruses are transmitted to humans through the bites of infective female Aedes mosquitoes. This is a day biting species, with increased biting activity for 2 hours after sunrise and several hours before sunset.

Mosquitoes generally acquire the virus while feeding on the blood of an infected person. After virus incubation for 8-12 days, an infected mosquito is capable, during probing and blood feeding, of transmitting the virus, to susceptible individuals for the rest of its life.

Incubation period

From 3 to 14 days, commonly 2-7 days. The virus circulates in the blood of infected humans for two to seven days, at approximately the same time as they have fever; Aedes mosquitoes may acquire the virus when they feed on an individual during this period.

Period of communicability

No direct person-person transmission. Patients are infective for mosquitoes from shortly before the febrile period to the end thereof, usually 3-5 days. The mosquito becomes infective 8-12 days after the viraemic blood-meal and remains so for life.

Susceptibility

Susceptibility in humans is universal but children usually have a milder disease than adult. Recovery from infection with one serotype provides lifelong homologous immunity but only short-term protection against other serotypes and may exacerbate disease upon subsequent infections.